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Microelectromechanical Systems (MEMS)

Microelectromechanical Systems (MEMS) research involves manufacturing extremely small mechanical elements, often integrated together with electronic processing circuitry. MEMS devices are manufactured in a similar fashion to electronic microchips. The biggest advantage here is not necessarily that the system can be miniaturized, but rather that the lithographic techniques that now mass-produce thousands of complex microchips simultaneously can also be used to manufacture mechanical sensors and actuators. As a result, the price of these components can be significantly reduced, as has happened with integrated circuits. Microengineering refers to the technologies and practice of making three dimensional structures and devices with dimensions on the order of micrometers to a few millimeters. The two constructional technologies of microengineering are microelectronics and micromachining. Microelectronics, producing electronic circuitry on silicon chips, is a very well developed technology. Micromachining is the name for the techniques used to produce the structures and moving parts of microengineered devices or making sensors with very small dimensions. One of the main goals of microengineering is to be able to integrate microelectronic circuitry into micromachined structures, in order to produce completely integrated systems (microsystems). Such systems could have have the same advantages of low cost, reliability and small size as silicon chips produced in the microelectronics industry.

The development of MEMS devices usually begins with silicon growth and wafer fabrication to produce wafers of known crystalline structure. After this the processes involved are highly dependant on the devices themselves. The most common sequence involves growing or depositing a thin film followed by lithography. Lithography is performed in order to place your mask set design onto the wafer surface. This is most often done using UV light and photoresist in a mask aligner to allow for multi-layer designs. With a sacrificial mask defining your devices, the wafers are then typically etched in order to pattern the thin film. There are many different methods of etching, including wet etching, dry etching and plasma etching. Once the sacrificial mask layer is removed this sequence can be performed again. There are many microfabrication issues such as topography, lateral etching, and adhesion when fabricating devices with micron resolution makes all the previously mentioned steps non-trivial. In Integrated Circuit (IC) fabrication, once all the layers have been fabricated the wafer can then be diced and packaged. This can also be done in MEMS fabrication once a proven manufacturing process has been developed. However, typically when performing research in MEMS the whole wafer is used to implement many different design variations.

Typical Process Flow